Data transmission and resolving system



April s, 1965 P. G. HANSEL ETAL Filed June 6. 1960 ATTO R N EYS April 6, 1965 P. G. HANSEL ETAL DATA TRANSMISSION AND RESOLVING SYSTEM Filed June 6, 1960 2 Sheets-Sheet 2 ATTO R N EYS rl`his invention relates to data transmission and .resolving systems and more particularly to systems which f transmit position or bearing data to a remote point and there resolve the data into analog voltages.

According to the latest Federal Aviation Agency staf tistics, there are thirty-live thousand miles of federal airways in use over the United States. This mileage is increasing constantly and very rapidly.

Due to this tremendous air mileage, it is extremely important to know the position of every aircraft at all times during Hight, and it is equally important to have this information in a form which is useful for computation and plotting.

It is, accordingly, a principal object of this invention to provide a data transmission and resolving system which provides rapid, accurate and useful bearing data.

`Another object of this invention is to provide an electronic circuit for resolving the bearing data into electrical ysignals having a predetermined relationship with bearing angle.

Brieiiy, the system of the present invention is comprised of three components. The first is a transmitter which modulates the amplitude of a carrier signal in accordance with both the bearing data and a reference pulse and transmits the resulting signal over either telephone ylines or a radio link. y A receiver located at a remote point is the second component in the system. The receiver separates the data and reference yinformation from the carrier and presents it to a third component, which may be, for example,

a visual display device, a data resolver, or other means. lf a data resolver is utilized, it converts the data and reference signals into analog voltages representing a desiredrelationship with the bearing angle such as the sine yand cosine.

Further objects and features of this invention will become apparent to those skilled in the art from a study of the detailed description of the invention which follows. Illustrating the various components of the invention and referred to in the description are the accompanying drawings, in which:

FIG. l is a block diagram of an overall bearing data y transmission and resolving system in accordance with the invention;

FIG. 2 is a block diagram of a transmitter used in the overall system shown in FIG. l;

FIG. 3 is a block diagram of a receiver used in conjunction with the system of FIG. 1; and

FIG. 4 Vis a block diagram of the data resolver which transforms a data signal into analog voltages.

The complete system for transmitting and resolving bearing data is shown in FIG. l. The direction finder will develop electrical signals which represent the position y or bearing of an object such as, for example,

a ship or an aircraft. The resulting signals are fed to a transmitter 12, the output of which is an A-M (amplitude modulated) signal containing both the bearing data and a reference pulse.

Thenr the A-M signal is transmitted to a receiver 14 by suitable means such as telephone lines, illustrated yschematically in FIG. l by the numeral 16, or by radio,

not shown. The receiver 14 separates the data and reference signals from the modulated carrier and feeds them United states Patent o" 3,177,478 Patented Apr. 6, 1965 ice via the leads 18 and 2.0 to a data resolver 22 and to a suitable indicator 24.

In the resolver 22, the data and reference signals are transformed into normalized D.C. voltages proportional to the sine and cosine of thepbearing angle. These D.C. voltages then form the analog input for a computer (not shown) which correlates the outputs of a plurality of such systems, the terminals 26 and 28 being provided for the connection of such a computer.

The indicator 24 may be any suitable display device such, for example, as a standard cathode-ray visual bearing indicator.

Transmission of the bearing or position data is accomplished by amplitude modulating a 200 c.p.s. (cycles per second) variable phase data signal on a 2400 c.p.s. carrier. The sidebands of 2200 and 2600 c.p.s. do not experience an appreciably different phase shift from that experienced by the 2400 c.p.s. carrier so that the data will remain stable in spite of severe variations in the transmission medium.

The 2400 c.p.s. carrier is used to represent a reference signal also. n Transmission of the reference in this form rather than in the form of a 200 cycle signal introduces an indeterminacy of phase mounting to an integral number of 30 steps. Resolution of this indeterminacy of the reference at the remote location is accomplished by `transmitting a non-ambiguous reference pulse, which pulse is transmitted vboth for initial set-up purposes and as a Calibrating feature whenever data signals are not being lated carrier is illustrated diagrammatically in simplified block form in FIG. 2. A 2400 c.p.s. square wave signal to be used as the carrier is available at the terminal 32 of the modulator 30, and the 200 c.p.s. data signal is applied to the modulator 30 through a setup switch 34.

The set-up switch 34 is any Suitable trigger circuit, as for example, a single-shot multivibrator. Therefore, when a data signal is delivered from the direction finder, the set-up switch 34 permits the signal to pass through to the modulator 30 and from there to modulate the carrier.

When the direction finder is producing no data signal, this condition is sensed by a suitable squelch circuit (not shown) incorporated in the tinder, and the squelch circuit sends a signal through the terminal 36 (FIG. 2) to the set-up switch 34. Upon receipt of this squelch or no-data signal, the switch 34 sends an enabling voltage signal to the gate circuit 33, which permits a reference pulse to pass from a terminal 40 to a grounding switch 42.

The grounding switch 42 preferably is another modulator which impresses a reference pulse upon the carrier 2(30 times a second. The reason for this is to resolve the phase indeterminacy created by using the 2400 c.p.s. signal as a reference.

The set-up switch 34 permits this latter modulation to take place, even though a subsequent data signal is received in the interim, by disconnecting the source of the data signal from the first modulator 30 for a given period. The output of the switch 42 modulated either by the data signal or the reference pulse, is passed through a butler amplifier 44 to achieve impedance equalization.

The tilter circuit 46 is connected to the output of the buffer amplifier 44 and serves t0 remove the harmonic content of the carrier. The output of the filter circuit 46 is the output of the transmitter 12 (FIG. 1), and this output is fed either to standard voice frequency telephone v lines or to a suitable transmitting antenna for transmission to a receiver 14 (FIG. l) located at a remote plot- Vcounter identified -by the numeral 6i). v

Sincevthe carrier signaljis ata frequency of twelve timesthat of thedata signal, (2400compared with200),' the ring of" twelve counter 60 will actuate a vreferenceV generator 66 at the proper timestoY obtaiuia reference trated vin greater detail in FIG. 3. n is fed simultaneously through the terminal 48 Ito three parallel circuits. f

In the first parallel circuit, a data detector 50 extracts i",

the 200 c.p.s."data signal '(if .one is present) and feeds it through a stopigate 52 directly to anv output terminal 54.

The received signal In the, absence of a data signal, however, the 'de-A y outputs of the discriminators tector 50 willY detectthe modulated reference pulse, Y

and it is4 necessary to `prevent a detected reference `pulse from beingfed out as a data pulse'at the terminal 54;V

v 8i)y and 82 will represent respectively the sine and cosine of'thebearing angle.

It is thought that the invention and its numerous Vvattendant advantageswill be .fully understood from the foregoing description, and it is obvious (that numerous modifications in addition to those'already disclosed, mayV ,be'mad'e` in the form, construction and arrangement of the several Aparts :Without departing from theuspirit or Vscope ofthe. invention or sacrificing any of its attendant advantages, thee forrns hereinbeing preferred embodiv ments for the purpose of illustratingthe invention.

Therefore, asecond parallel Vcircuit contains a pulsev modulation detector 56, the output of which will close the gate'SZ thus preventing.the;reference pulses :detected by the data detector 50 from appearingat the output terminal 54 as data signals. f To obtain'a reference signalof thesame low frequency as that of the datal signal, the 'signal received at terminal Y 48 is fed' simultaneously `to a third parallel circuit con.`

taining a 2.4 kc. limiter identified in FIG. 3 by the'numeral 58. Y'lhelir'niterfSS removesfall modulation from the receivedsignal before passing it on' to a ring of twelve signal of 200,c.p.s. at the output terminal 678.` The syn-V chronization'of the vring counter 60 is accomplished .in a manner now to beY described; Y'

Whenever a pulse detectedV by ,the pulse modulation 'i detector 56 is not time coincident with the; reference pulse f Having thus; l,fully .described the invention, what is 'j claimed'as new vand desired tof be 'secured by Y.Letters Patentof the United States is:

f 1,'A data transmission andA resolving system com-g` 'Y prising meansY to'developelectrieal data signals representative of the position of an object,means for transmittingsaidelectrical data signals with a reference pulse f .in thel form lofan' amplituder modulated carrier, said transmitting means including a iirst modulator for modulating said carrier in accordance with said data signals and a secondl modulatorrfor modulating said carrier in accordancewithV said referencepulse, said` transmitting Vmeans'further controlling said first modulator to allow4 operation. thereof only in the presencejof saidk datasignal and means forcontrolling said second modulatorto ,Y Y 'allow operation thereof only'in the absence of said data signal, receiving 'means for separating said electrical data` -v signal-'from saidreferencesignal, and means for resolvingy said datarsi'gnalv intoV analogs having a predetermined relationship With'the position of said object.

from the ringrcounter 60, stop gate 62.will Vnot actuate stop gate 64'which will then act to block one'of the pulses A from the limiter 5S, thusl stepping the V'counter backwards.

This operation continues untillfstopjgate 62 prevents further-interference with thel ring counter 60;l V,This 'will 12. Afdataftransrnissionand resolving system'` asset Y Y forth in claim 1-wherein thev transmitting means further occur as soonas a reference pulse'emitted bythe ring counter 610 is coincidentrwith pulsereceived from pulse modulation detector 56, ,Y y i i Y,

' The circuits just Vdescribed will continue to monitor the operation ofthe ring counter w60to prevent momentary line failures from permanently upsetting the operation of v the unit. At the proper times, however, the ring counterv 60 will, actuate the reference generator 66 to provide 'a reference signal of 200Vc.p.s,`at the outputjterminal A68.

`Both* the data and reference signals arethen fed to a suitable utilization circuit such iaseither a visual display device oria data resolver.

FIG. 4 illustrates a circuit `totv transform the? vdata Y and reference signals` ofthe receiver` 14 toy analogs lof the sine and cosine of the bearingangle. The ydata. signal limiter circuit 72 and an amplitudedetector 74.' "The obf includingrneans to iilterrthe-harmonic content from said modulated carrier.

f 3`.*A.datatransm1ssion and resolvingsystern as set forth jin claim ll whereinthe receiving means comprises a first i Y detector to detect bothithe data signaland. thereference pulse, aY second detector vtodetect'only the referencer. pulses, a' limitingkcircuit, forobtaining av modulationfree carrierV signal, a gatingcircuit connectedfto both said `first and said second detectors forallowingfonly'the data signal `to. pass, agscaling Ycircuitconnected to said Y limitingY circuit,-the ratio' of said4 scaling vcircuit being equal to the ratio of the frequencies -of the carrier and n 'the Vdata signal, means for synchronizing said scaling` circuit with lsaid second detector, andY generating means connected to saidscaling circuit to -provider'aV reference 'taken through theterminal 70 is fed simultaneously to a Y ject of these circuits is to remove from the data signal amplitude variations due to elevation angle or threshold signal, in other words, Vto normalize the amplitudes Vof the dataj signalpfThis normalization is accomplished that its output undergoes only negligible phaseand Yamplitude variation with normally expected variation in inputlevel.`

` primarily bythe limiter circuit '72'which'is ydesigned so Itis necessary also to use a squelch circuit 76 to 'limit j noise. Y

The fundamentalcanrbe,extracted from'the output of Y thelimiter72by alter circuit 78 which is designed tof protect against phase shift. Thev normalized dataksignal' solobtainedois vfed then to phase .discriminators 80.

and 8,2.V Y

quadrature. J

signal 1 of thesame frequency Yas that of the data signal.

4.' Al 'data transmission and resolving systemras set forth in claiml wherein .the resolving `means comprises la first phase discriminator, aV secondl phaserdiscriminator, means to limit thel amplitude` of the data signal', means Vto iilter'the'data signa1,.means to apply said'data rsignal Vto saidlfirsrt phase-Vdiscriminator yand simultaneously to `said secondVV phase discriminatoi-and means'to operate saidfiirst andy second phase discriminator in Velectrical f 5.' Aidata transmission system comprising input means "60 for receiving electrical datasignals, a carrierl signalfgenerator'for producing a carrier signal output, a modulator coupledbetween said input means and said'carrier'signal generator forV modulating said carrier signal output in accordance with said electrical datal signals, reference signal 'means coupled to said modulator for' modulating. saidcarrierrsignal in accordance withareference signal,

receiver means for 1 receivingv saidmodulated carrier signal to separate the"data`si'gnal modulation thereon from l the'refe'rence signal modulation thereon, and data"resolvingk means "for, developinggioutputjsignals, said resolving means .including first 'and'. second lphase discriminators coupled toY receive said reference signal information from said receiver meansfsaid resolving means further" includi ing means coupledV toireceive said data information Yto .normalize the amplitude,v thereof'anddeliver the same to each of said phasevdiscriminators, whereby D.C. output signal components of said data signals are developed at the output terminals of each of said phase discriminators.

6. The combination defined in claim 5 wherein said modulator contains a rst modulating means and a second modulating means, said rst modulating means being coupled to said input means and said second modulating means being coupled to said reference signal means, and also including modulator control means coupled to said input means and to said modulator, said modulator control means actuating said rst modulating means only in the presence of said data signals and actuating said sec- 6 ond modulating means only in the absence of said data signals.

References Cited in the file of this patent UNITED STATES PATENTS 2,579,831 Keinath Dec. 25, 1951 2,719,284 Roberts Sept. 27, 1955 2,730,696 Davis Jan. 10, 1956 2,736,007 Kenyon Feb. 21, 1956 2,970,302 Gridley Jan. 31, 1961 

1. A DATA TRANSMISSION AND RESOLVING SYSTEM COMPRISING MEANS TO DEVELOP ELECTRICAL DATA SIGNALS REPRESENTATIVE OF THE POSITION OF AN OBJECT, MEANS FOR TRANSMITTING SAID ELECTRICAL DATA SIGNALS WITH A REFERENCE PULSE IN THE FORM OF AN AMPLITUDE MODULATED CARRIER, SAID TRANSMITTING MEANS INCLUDING A FIRST MODULAR FOR MODULATING SAID CARRIER IN ACCORDANCE WITH SAID DATA SIGNALS AND A SECOND MODULATOR FOR MODULATING SAID CARRIER IN ACCORDANCE WITH SAID REFERENCE PULSE, SAID TRANSMITTING MEANS FURTHER CONTROLLING SAID FIRST MODULATOR TO ALLOW OPERATION THEREOF ONLY IN THE PRESENCE OF SAID DATA SIGNAL AND MEANS FOR CONTROLLING SAID SECOND MODULTOR TO ALLOW OPERATION THEREOF ONLY IN THE ABSENCE OF SAID DATA SIGNAL, RECEIVING MEANS FOR SEPARATING SAID ELECTRICAL DATA SIGNAL FROM SAID REFERENCE SIGNAL, AND MEANS FOR RESOLVING SAID DATA SIGNAL INTO ANALOGS HAVING A PREDETERMINED RELATIONSHIP WITH THE POSITION OF SAID OBJECT. 